Such instruments are primarily used for a single task, i.e., only for the removal of the defective heart valve, but instruments of this type are also known that include additional functions, which make it possible, for example, to insert a new heart valve with the same instrument and in the same surgical procedure after the removal of the defective heart valve (see DE 600 17 189 T2, FIG. 1 therein, reference number 10 with the description belonging thereto).
It is also known to provide instruments of this type with catching devices and/or with filter screens that can be clamped on, for example, in order to prevent fragments of tissue that are freed during the surgical removal of a defective heart valve (which is also usually calcified) and/or material deposits from entering the bloodstream of the patient (see the above-named DE 600 17 189 T2, FIG. 1 therein, reference number 14 with the description belonging thereto).
All of these embodiments of the instruments always have as a basic function the removal of a defective heart valve, so that the invention described below can be basically applied to these instruments.
Also, the invention described below is independent of the respective surgical method by means of which the instrument is guided to the defective heart valve by its advancing (distal) end. This is true for both conventional surgical methods, which presume the opening of the thorax and the exposing of an access to the heart, as well as for surgical techniques that make possible a heart valve surgery with a far smaller stress for the patient with the use of catheters and endoscopes (so-called minimally invasive methods).
A method is also known as a minimally invasive surgical method, in which an instrument can be inserted according to the invention, in which a trocar, which is used as an instrument channel, is guided directly to the heart between the ribs of an unopened thorax and is moved through the muscle of the heart wall up to the defective heart valve, so that surgery can be performed via the trocar on the beating heart “pump” (i.e., without the connection of a heart-lung machine (see for this purpose U.S. Pat. No. 5,924,424).
The present invention proceeds from a prior art instrument, as is known from US 2005/0075659 A1 of instruments for the surgical removal of a defective heart valve (see therein FIGS. 2A to 2C with the description relating to it on page 2 starting with paragraph number [0037]).
The known instrument has two halves or body members arranged at an axial distance relative to one another at or on a guide rod or elongated member, and each body member is formed in the shape of a spirally wound cutting element around the axis of the instrument. The two body members can be moved axially relative to one another by means of the elongated member in such a way that their spiral cutting elements that are aligned opposite one another cut out a defective heart valve positioned between the two body members.
For the surgical introduction of the instrument into the surgical field, the spirally wound cutting elements can be collapsed radially, i.e., the cutting elements that are somewhat loosely wound in their initial form will be tightly wound, whereupon the radial distance between the outer winding and the instrument axis becomes small, and a contact protective sheath, which is narrow in diameter and fitted to the elongated member, can be moved onto the two body elements. This has the principal advantage that the advancing (distal) end of the instrument comprising the narrow, fitted contact protective sheath is moved through the defective heart valve by the width of the piece relatively without problem until it is in a position, in which one body member is found on one side of the defective heart valve and the other body member is found on the other side of the defective heart valve. Then the contact protective sheath is pulled off axially from the body members in this position of the instrument, so that their spirally wound cutting elements can be released. In this way, the radial distances between the spiral windings increase from the instrument axis until a diameter is achieved for the respective outer winding of the cutting element, which corresponds to the diameter of the defective heart valve to be cut out and to the diameter of the new heart valve that is subsequently to be surgically inserted.
The two body elements are then moved toward one another by means of the elongated member (to which one of the body elements is attached) and are guided by means of a tubular member for displacement on the elongated member (the other body element is attached to this tubular member) and the defective heart valve is cut out. Then the two body members can be rotated relative to one another in order to support the cutting process.
After cutting out the defective heart valve, the spiral cutting elements are brought back to their smaller radial diameter and the contact protective sheath is again moved onto the two body members, and this is done, in fact, prior to removing the instrument from the surgical field. Problems may occur when the contact protective sheath is again moved onto the two body members, since despite identical manual manipulations, spirally wound cutting elements may have different spiral configurations and thus different outer diameters. Reference is made to U.S. Pat. No. 5,924,424 (see page 3 therein under paragraph number [0041]) relative to this disadvantage of the known instruments.
Another disruption in the functionality of the above-named instruments results from the fact that the spirally wound cutting elements do not produce a geometrically circular cut, whereupon the subsequent surgical insertion of a new heart valve is made considerably difficult, especially since currently all mechanically produced heart valve prostheses have a circular base for attachment.
It is also a considerable disadvantage that the spirally wound cutting elements of the known instruments of this type do not cut out a defective heart valve as a one-part valve piece, but the valve piece is primarily “chipped off” between its spiral cutters. In this way, additional problems arise and it is necessary to arrange catching devices and/or filter screens in order to prevent the “chipped off” tissue fragments from entering the bloodstream of the patient.